Japanese Kokai Patent Application No. 2007-55691, for example, discloses a device for preventing travel of an elevator car with the doors open. In the case of the technology described in that document, a door detection switch detects the state of the doorway, a car position detector detects the position of the car, and a fall-prevention means detects travel with the doors open based on outputs from them. A rope gripper, which is used to hold a rope for hanging the car, is activated when said fall-prevention means has detected travel of the car with its doors open in order to prevent further traveling of the car.
One drawback of such an arrangement is that it relies upon software-based processing and if it fails, the car may be moveable with the doors open.